The connected device controls the output voltage, you would use a cable configured to "tell" the power bank to supply it with 12v.
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I don't think anything 'guarantees' the power bank won't provide a different voltage, just the presumption/expectation that the devices will work as designed.
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To power an FT-817 type of radio with 12 volts, you would use a cable designed to priced the desired voltage, like this:
https://a.co/d/hNy4MWO
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Hope this helps,
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Ken, N2VIP
